Help to buld complex query

[Henrique]

I have two tables:

Counters:' Every 10 minutes a record is added with updating the counter

Data_Hora ID_Contador E_SVazio
23-04-2010 0:00 CTE003 16.528.690
23-04-2010 0:00 CTE002 21.527.520
23-04-2010 0:10 CTE003 16.528.750
23-04-2010 0:10 CTE002 21.527.570
23-04-2010 1:20 CTE003 16.528.800
23-04-2010 1:20 CTE002 21.527.620
23-04-2010 1:30 CTE003 16.528.850
23-04-2010 1:30 CTE002 21.527.670
23-04-2010 2:40 CTE003 16.528.890
23-04-2010 2:40 CTE002 21.527.720

Data counters:
ID Nome Uni_Fab PT Zona Equipamento
CTE001 XPT0 Zebra PT1 Banhos Caixa1
CTE002 XPT1 Xoli PT2 Banhos Caixa2
CTE003 XPT2 Xoli PT1 Banhos Caixa3

Query:

SELECT
convert(varchar(2), contadores.Data_Hora, 108) as Hora,
Sum(MAX(E_SVazio) - MIN(E_SVazio)) as H_SVazio,

Contadores JOIN DadosContadores ON Contadores.ID_Contador =
DadosContadores.ID
WHERE
Year(Data_Hora)= 2010 AND Month(Data_Hora)= 4 AND Day(Data_Hora) = 23 And
E_SVazio<>0 AND Uni_Fab = 'Xoli'
GROUP BY
Year(Data_Hora),Month(Data_Hora),Day(Data_Hora),Convert(varchar(2),
contadores.Data_Hora, 108)
ORDER BY
Convert(varchar(2), contadores.Data_Hora, 108) Asc

This query d'ont whork whel

What I want is the sum of the energies, which is given by the difference of
two readings (Min and Max) to 23/04/2010 and Uni_Fab = Xoli grouping.

example:
"xoli" has two counters CTE002 and CTE003 and need to know the sum of these
two counts

someone help me?

Thanks

Se