failure on controlling Alicat Flow Regulator

I am a new user of Alicat and have a problem on realising the communication between MFC and arduino. The physical connection is as following: Arduino->Arduino RS232 shield->RS232 DB9 connector->Alicat MFC.

Beforehand the Arduino did communicate with Alicat ---unit ID can be changed with the following code:

void setup() { // put your setup code here, to run once: Serial.begin(9600); Serial2.begin(9600);

Serial2.write("w91=50"); Serial2.write("\r"); Serial2.write("@=@"); Serial2.write("\r");

Serial2.write("\r"); Serial2.write("\r"); Serial2.write("\r"); Serial2.write("*@=Q"); Serial2.write("\r");

}

void loop() { }


Later, someone borrowed it from me and returned to me. Again, I tried the same thing with the whole setting but with the new RS232 DB9 connector replaced, the communication fails.

I am wondering if this failure is to do with some settings of alicat itself related to RS232 communication. I really need your wise suggestion on this. Thank you in advance.